Looks like your TV has the proprietary OneConnect module from Samsung. If that's the case, I recommend this setup:
Xfinity Box ==(HDMI)=== Onkyo HDMI 3 (cbl/sat)
Onkyo HDMI Out ]==(HDMI)==[ Samsung OneConnect HDMI 3 (ARC),
and use the OneConnect cable to link to your TV. Your receiver will be the brains of your system, and other HDMI devices should pass through here.
In the alternative, you can also connect the cable box to the One Connect HDMI 1 (STB ) Instead of the Onkyo. Doing this will make your Samsung the brains of your home theater system, and you should connect other devices through the Samsung.
"Sometimes the best way to learn something is by doing it wrong and looking at what you did." - Neil Gaiman